As is widely known, a golf ball may be formed by using a forming mold that can be divided into two parts, the mold, having a spherical cavity therein, is formed with a large number of protrusions for forming dimples (dimple forming protrusions) on the wall surface of the cavity, and has a parting line substantially at the position of the equator of the cavity.
In the case in which the mold is of an injection molding type, on the parting line thereof, forming material injection gates for injecting a cover material (resin material) for a ball are provided at equal intervals on the circumference. On a ball formed by cover material injection, the cover material having hardened within the gate remains in a projecting state, forming protrusions, and in addition, fine burrs are also produced at the parting line position of mold. The protrusions and burrs on the parting line are removed by grinding after formation.
In recent years, there have been proposed various kinds of seamless golf balls in which dimples are arranged even on the parting line (usually, coinciding with the equator line of the ball). These seamless golf balls have excellent flying performance because the degree of freedom of dimple arrangement is high so that dimples can be arranged evenly with high density on the surface of the ball.
For the above-described seamless golf ball, unfortunately, when the protrusions and burrs on the parting line are removed by grinding, the dimple portions (especially, dimple edge portions) are ground at the same time. As a result, the dimples are made shallow, which is undesirable. Therefore, there arises a problem in that the inherent ball performance is deteriorated and the appearance is also marred.
Also, the deformation of dimples due to grinding is sensitive to the degree of grinding, so that variations between golf balls have occurred.
The specification of Japanese Unexamined Patent Application Publication No. 11-114092 describes a method of forming protrusions near the dimples on the equator to avoid abrasion of dimples due to grinding.